Control apparatus for wet oreprocessing system



Nov. 17, 1970 D. wEsTo'Ny 3,541,593

CONTROL APPARATUS FOR WET ORE-PROCESSING SYSTEM -f-ff 5-@w l A A Sm l15H/131.1 l l' .5H SL $62 Sca 5c4 D. WESTON Nav. 17, 1970 CONTROLlPPRATUS FOR WET ORE-PROCESSING SYSTEM uGm @SG AQSSWQ CONTROL APPARATUSFOR WET OREPROCESSING SYSTEM Filed Feb. 13, 1967 D. w'sToN Nov. 17, 19705 Sheets-Sheet L .vhmi

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Ll Ll L.. nr i uw Nov. 17, 1970 CONTRGL APPARATUS FOR WET ORE-PROCESSINGSYSTEM Filed Feb.` 13, 19s? /m/E/vrol? m//a Wfsm/v ggg; @mdf 5WArme/vers United States Patent O 3,541,593 CONTROL APPARATUS FOR WETORE- PROCESSING SYSTEM David Weston, Toronto, Ontario, Canada, assignorto Aerofall Mills Limited, Toronto, Ontario, Canada Filed Feb. 13,`1967,Ser. No. 615,755 Claims priority, application Canada, Nov. 18, 1966,

Int. Cl. B03b 13/00;104c 11/00; F15b 5/00 U.S. Cl. 209-211 9 ClaimsABSTRACT OF THE DISCLOSURE The automatic control of slurry pressure incyclone classifiers by sequentially opening or closing selectedclassifiers to ow of slurry therethrough.

BACKGROUND OF THE INVENTION In the processing of ore, it is common tomix the ore with water or another suitable liquid and, following one ormore grinding operations, to separate coarse ore particles from fine oreparticles using cyclone classifiers.

The cyclone classifier, by means of centrifugal force, separates fineparticles from coarse particles in a wet slurry. The coarse particlesare forced toward the outside wall of the cyclone classifier and proceeddownward to the underflow while the fine particles tend to remain in thecenter of the classifier and rise with the overow output from the top ofthe classifier.

The manner in which a cyclone classifier behaves is affected by the rateof flow of slurry through the classifier and by the pressure of theslurry entering the classifier. If rate of flow is increased at constantpressure, or if pressure is increased at constant rate of flow, finerparticles tend to be forced to the outside wall and to flow out of theunderfiow discharge with the result that the overflow has proportionallyfewer particles and a proportionally greater quantity of liquid so thatthe overow slurry density decreases. The converse of the above statementis also true. lf pressure or rate of flow decreases, coarser particleswill enter the overfiow and the overfiow slurry density will increase.

The change in the pressure at the input of each classifier will vary asthe square of the change of the rate of fiow through the classifier. Therate of flow in the system as a whole can be affected in many ways, someof which are:

(a) Variation in the output of a pump controlling a sump level;

(b) Variation in the amount of water entering a sump as an input;

(c) Variation in the feed rate of fresh unprocessed material into thesystem.

It has been found in practice that in order to maintain efficientcyclone classification, the pressure of the slurry input to theclassifier shouldbe maintained within a predetermined range.

In many ore-processing operations, two or more grinding stages areused-a first grinding stage for reducing the size of the input rawmaterials, and one or more additional grinding stages receiving thefines from the first grinding stage and regrinding these to producestill finer particles. In such operation, cyclone classifiers may beemployed to separate, in the output of the first grinding stages, the

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coarse particles from the fines. The fines, or the more coarse of thefines, are transported to the'secondary grinding stage or stages whilethe coarse particles are fed back into the input of the first grindingstage'so that they may be further reduced in size before beingtransmitted to the secondary grinding stages. The underflow of thecyclone classifiers is therefore fed as an input to the first grindingstage and the overfiow of the cyclone classifiers is usually fed into acollecting sump or surge tank. The slurry in the collecting sump ispumped as an input into the secondary grinding stages.

In such systems as the foregoing, it is common to pro- I vide a densitycontrol device for controlling the density of slurry fed into thesecondary grinding stages. The density control device senses the densityof the slurry flowing from the output of the pump and controls theamount of liquids (usually water) fed as an input into the collectingsump. As the slurry density increases, the amount of water inputincreases correspondingly to reduce the density of the slurry in thesump. Similarly, as the density of the slurry decreases, the rate offlow of water into the collecting sump decreases so that the slurrydensity will increase.

For efiicient operation of systems such as the foregoing, it has beenfound that it is desirable to have the secondary grinding stages operateat maximum efficiency and to adjust the operating parameters of theprimary stage so as to make possible the efficient operation of thesecondary grinding stage or stages. This implies that the level anddensity of slurry in the collecting sump should be more or lessconstant. As indicated above, the level of slurry in the collecting sumpis determined partly by the rate of fiow of water input into the sumpand partly by the overfiOw of the cyclone classifiers leading into thecollecting sump. The water input into the collecting sump is, as statedabove, controlled by the density control means. Accordingly, the problemremains of controlling the overfiow from the primary stage cycloneclassifiers. If the quantity of ore in the cyclone classifier overfiowis greater than the amount of slurry that the secondary grinding systemcan handle, the level of the collecting sump will increase and theamount of ore in the overflow will have to be reduced. Conversely, ifthe overfiow from the cyclone classifiers contains too little ore, thelevel of slurry in the collecting sump could decrease so as to reducethe efficiency of the overall ore-processing operation.

In general, an efficient ore-processing system requires anefficiently-operated secondary (ne) grinding stage and a primarygrinding stage that can act as a surge with respect to the secondarystage. Both primary and secondary stages must be provided with controldevices to maintain system parameters within efficient operating limits.Prior to the present invention there has been no means for automaticoverall control of the control devices in both primary and secondarystages to promote their efficient interaction.

SUMMARY OF THE INVENTION It is accordingly an object of the presentinvention to ,provide means for automatically controlling, withinpredetermined limits, the pressure of the slurry introduced into cycloneclassifiers used in an ore-processing operation.

According to the present invention, the apparatus for controlling thepressure of a slurry introduced into a plurality of cyclone classifierscomprises a plurality of control valves each respectively associatedwith a corresponding one of said cyclone classifiers, permitting slurryto flow through any given one of the classifiers when its associatedcontrol valve is open and blocking fiow of the slurry through any one ofthe cyclone classifiers when its respective control valve is closed. Apressure transducer responsive to the pressure of the slurry at theinput to the classifiers produces a signal representing the slurrypressure and a pressure comparator responds to this signal so as toproduce a high pressure signal when the slurry pressure reaches apredetermined high pressure and produces a low pressure signal when theslurry pressure falls to a predetermined low pressure. Valve closingcontrol means respond to the low pressure signal so as to close one ofthe valves when the low pressure signal is present, and valve openingcontrol means respond to the high pressure signal so as to open one ofthe valves when the high pressure signal is present.

If, after a predetermined delay interval following closing of a valve,the low pressure signal is still present, the valve closing controlmeans closes another one of the valves. This operation repeats itself aslong as the low pressure signal remains and as long as there remain somevalves to be closed. Similarly, if, after a predetermined delay intervalfollowing opening of a valve the high pressure signal remains, thevalve-opening control means opens still another valve. This operationrepeats itself until all the valves are open. It is usually necessary toprovide delay means to render inoperative the valve control meansimmediately following opening or closing of the valves because theopening or closing of a valve gives rise to a transient pressure drop orrise, as the case may be, which could stimulate the pressure comparatorinto nullifying the previous valve opening or closing because of thetransient presence of a low pressure or high pressure signal, as thecase may be. In order to eliminate the undesirable efect of thetransient pressure change, the delay means operates so that the systemcan adjust to steady state operation before any further valve operationis effected.

RESUME OF THE DRAWINGS FIG. l is a schematic diagram of a cyclone headerincluding its valves and the related control system according to theinvention;

FIG. 2 is a schematic flow diagram showing two stages of an oreprocessing system employing control apparatus according to theinvention;

FIG. 3 is a schematic diagram of a preferred arrangement of overridecontrols according to the invention;

FIG. 4 is a block diagram of an ore processing system using controlapparatus according to the invention;

FIG. 5 is a schematic plan view of a plurality of cyclone classifiersarranged around a central cyclone header, which may be used in thesystem of FIG. 2;

FIG. 6, found on the same sheet of drawings as in FIG. l, is a pressuregraph used to explain the pressure control system and level controlsystem according to this invention;

FIG. 7, on the same sheet of drawings as FIG. l, is a circuit diagram ofa preferred embodiment of a programmed timer for use in the system ofFIG. 4, according to this invention; and

FIG. 8 is a circuit diagram of another preferred embodiment of aprogrammed timer for use in the system of FIG. 4 according to thisinvention.

DETAILED DESCRIPTION REFERRING TO THE DRAWINGS FIG. l illustrates inschematic form the pressure control device according to the invention. Afiuid in an input conduit 10 is distributed via a distributor 11 touncontrolled conduit 12 and controlled conduits 14, 16, 18 andrespectively. The conduits 12, 14, 16, 18 and 20 are connected to acommon input (namely the distributor 11). Only four controlled conduitsand four uncontrolled con- 4 duits are shown in FIG. l, by way ofexample, but it is understood that any desired number of controlled anduncontrolled conduits may be provided.

The controlled conduits 14, 16, 18 and 20 have mounted therein valvesV1, V2, V3, and V4 respectively. According to the invention, thepressure of the fiuid in input conduit 10 is controlled by opening orclosing one or more of the valves V1 through V4 inclusive. Thus, if thepressure in input column 10 is too high, one or more of the valves V1,V2, etc., can be opened so as to provide additional routes for theescape of Huid from the distributor 11, thereby reducing the pressure inthe input conduit 10. Likewise, if it is desired to increase thepressure in the input conduit 10, one or more of the valves V1, V2, V3,V4 may be be closed so as to decrease the number of routes through whichfiuid may leave the distributor 11. It is contemplated that in thesystem shown in FIG. l, normal operation will require that two of thevalves' be opened and two closed. It is further contemplated that thepressure variations in the input conduit 10, will, in almost all cases,be rectifiable by the opening or closing of no more than two additionalvalves. If the case were otherwise, more controlled conduits should beprovided.

The valves V1 to V4 are controlled as follows:

A pressure sensor 22 is mounted on the input conduit 10 or distributor11 at any convenient place. The pressure sensor 22 is adapted to producean output signal representative of the pressure in input conduit 10.This output signal is received as an input by a pressure comparator 24which is adapted to generate a high pressure signal when the pressure inthe input conduit 10 rises above a predetermined pressure and is adaptedto generate a low pressure signal whenever the pressure in the inputconduit 10 falls below a certain predetermined pressure. The highpressure signal is applied via a delay device 30 to a valveopeningdevice 28 and a low pressure signal is applied, also via the delaydevice 30, to a valve-closing device 26. It is to be understood that thedevices 26 and 28 may be combined in a single valve control device, butare shown separately in FIG. 1 for explanatory purposes. Thepredetermined high and low pressure limits can be taken as predeterminedpressure differences with respect to a pressure standard. For somepurposes it is convenient to permit adjustment of these limits, and forsuch purposes pressure standard adjustment means 25 is provided foradjustment of the pressure standard, and thus for the adjustment of thehigh and low pressure limits. The specific details of the adjustmentmeans 25 are not per se part of the present invention, and obviously maytake many forms depending upon, e.g., the parameter chosen to govern thepressure standard adjustment. The means 25 may obviously be integralwith comparator 25; in the simplest case, the pressure standard may be adial setting in the comparator 24.

In response to a high signal, the valve-opening device 28 opens apredetermined one of the valves V1 through V4. This results in theprovision of an additional conduit through which fiuid may fiow out ofthe distributor 11, and therefore the pressure in the input conduit 10is reduced.

Similarly, if a low pressure signal is generated by the pressurecomparator 24, the valve-closing device 26 closes a predetermined one ofthe valves V1 through V4 so as to block off one of the conduits leadingfrom the distributor 11 and therefore to increase the pressure in theinput conduit 10.

It can be seen that opening a valve has the effect of immediately oralmost immediately reducing the pressure in the input conduit 10. In theabsence of any delay means, the transient reduced pressure could besensed by the pressure sensor 22, and passed on to the pressurecomparator 24, which might then generate the low pressure signal havingregard to the transient reduced pressure. (Under steady stateconditions, however, the low pressure signal should not be produced-thesystem should be designed so that opening or closing a valve produces asteady state change not sufficient to bring the pressure to the oppositepressure limit). The transient W pressure signal, however, would resultin the closing of the valve that had just been opened, cancelling outthe desired opening operation. Accordingly, the delay device 30 isincluded in the system so that the foregoing undesired transientoperation does not occurfTo this end the feed-back paths 32 and 34leading from the valveclosing device 26 and the valve-opening device 28respectively operate the delay means 30 whenever the valve-operatingdevices open or close one of the valves. The delay device 30 theninterrupts the signal from the pressure comparator 24 to thevalve-operating devices 26 and 28 so that notwithstanding the productionby the pressure comparator 24 of a high pressure signal or low pressuresignal, neither of the valve-operating devices will operate.

The time intervals during which the delay switch 30 is operable willdepend upon the system Whose pressure is desired to be controlled.Basically, it is required that the delay interval be long enough so thatthe system has ample opportunity to return to its steady state. Then, ifafter having reached a steady state, the pressure in the system is stilltoo high or too low, the pressure comparator will continue to generateeither the high pressure signal or the low pressure signal, as the casemay be, and a further valve may be opened or closed.

The valve-operating devices 26 and 28 adapted to operate the valves V1through V4 sequentially. In steady state operation, let us suppose thatthe valves V1 and V2 are opened and the valves V3 and V4 are closed.Then, for example, too great an increase in pressure would result in theopening of the valve V3, and if after the delay interval had elapsed,the pressure were still too high, the valve V4 would be opened.

Likewise, if the pressure in the conduit 10 decreases, the valve-closingdevice 26 closes irst the valve V2 and, if the pressure decreasepersists after the delay interval provided by the delay device 30,closes the valve V1 so as to increase the pressure in the input conduit10.

As mentioned above, as many controlled conduits may be provided as arenecessary to cope with the pressure changes in the system. While in mostcases approximately the same number of valves will be open as are closedduring normal operation, there may be instances in which the systempressure rises above normal by (say) 50% but never falls below normal bymore than (say) 10%. In this case, there should be more closed valvesthan open 'valves during normal operation so that both the expectedpressure increases and expected pressure decreases can be handled by thesystem.

Where the fluid whose pressure is desired to be controlled is the slurryinput to cyclone classiers in an ore-processing system, the slurry inputwill be applied to the conduit -10 in FIG. 1, the distributor 11 in FIG.1 will correspond to the cyclone header, and the conduits 12, 14, 16, 18and 20 will lead to respective cyclone classifiers.

FIG. 2 is a flow chart illustrating the automatic control according tothe invention, of two grinding stages of an ore-processing system.

The primary grinding stage includes primary grinder P14 to which ore isfed from an ore input P16. The output of the grinder is fed to one ormore separators P18 which separate the waste products from usable ore.The usable ore is fed as an input to a collecting sump P12.

A pump P20 pumps the slurry from the collecting sump P12 through adensity controller P22 to a plurality of cyclone classifiers P24. Thecyclone classifiers may be arranged in the manner illustrated in FIG. 3and comprise both uncontrolled classiers which pass slurry under allconditions and controlled classifiers provided withgvf'alves enablingslurry to be passed through selected ones of such classifiers havingtheir respective valves open. The valves are opened and closedsequentially in response to pressure conditions prevailing at thecyclone header 56 (FIG. 5) in the manner previously described withreference to FIG. l.

The overflow output from the cyclone classifiers P24 contains the fineswhich are transmitted as an input to a collecting sump S12 of thesecondary grinding stage. The underllow from the cyclone classifiers P24containing the coarse particles is fed back to the primary grinder P14for further grinding.

The primary grinding stage includes three control devices, viz, thedensity controller P22, a pressure controller P26, and a pump controllerP28.

The density controller P22 may be of a conventional type known in theart, using a sensing element, for example, a gamma gauge responsive togamma radiation. The density controller P22 regulates a valve P30 on thewater input P32 leading into the collecting sump P12. If the densitysensed by the density controller P22 is too low, the controller P22partially closes the valve P30, permitting less water to pass, therebyincreasing the ratio of solids to liquids in the collecting sump P12.Similarily, if the density controller P22 senses a solids-to-liquidsratio which is too high, it opens the valve P30 to permit more water tofiow into the collecting sump P12 thereby tending to reduce the densityof the slurry.

The pressure controller P26 comprises the pressure comparator, valveopening and valve closing control device, and delay unit described withreference to FIG. 1. Thus, the pressure controller P26 opens a valve topermit an additional cyclone classifier to pass slurry if the pressurein the cyclone classifier distributor becomes too high. Likewise, thepressure controller closes a valve thereby cutting off a cycloneclassifier, whenever the pressure in the cyclone header becomes too low.Por example, assuming cyclone classifiers of 15 inches in diameter, itmay be desired to regulate the pressure in the cyclone classilierdistributor between 14 and 16 p.s.i. If the pressure reaches 16 p.s.i.,the pressure controller opens a valve; if the pressure drops to 14p.s.i., the pressure controller closes a valve.

It will be noted that in PIG. 5, eight uncontrolled and four controlledcyclone classifiers are shown. Assuming that all the valves are closed,only eight cyclone classiiers pass slurry. If the pressure in thecyclone header rises to 16 p.s.i., the opening of an additional valvewill increase the number of conduits conducting slurry from eight tonine. The result is that a pressure drop of the order of 2 p.s.i. (andas a practical matter, somewhat less) occurs. The pressure drop willreduce the pressure prevailing in the system to something just greaterthan 14 p.s.i. It will be noted that the opening of closing of a valvedoes not tend to change the pressure in the system so much that theensuing steady state operation would result in a pressure outside the 14to 16 p.s.i. limits. If there were too few uncontrolled cycloneclassiiers in the system, or if the pressure differential between thepermitted high and permitted low pressures were too small, the openingof a valve could lead to a steady state condition in which the pressurewas too low, which would result in the re-closing of the valve as soonas delay period had expired; similarly, the closing of a valve would,after steady state was reached, result in a pressure which would requirethe opening of a valve. This hunting oscillation of the system shouldgenerally be avoided; the designer of the system should ensure that thenumber of uncontrolled cyclone classiiiers is sufcient that the openingor closing of a valve on a controlled classifier Will not cause anensuing oscillation.

If the number of uncontrolled classifiers is suiiiciently large, and ifthe pressure differential between the permitted high and permitted lowpressures is sufficiently large, it may be possible in some systems toeliminate the delay device described with reference to FIG. 1 alto- 7gether. However, in most applications, the transient effect caused bythe opening or closing of a valve will be sufficient to warrant theinclusion of the delay device.

The pump controller P28 may be of a conventional type known in the artusing, for example, an eddy current clutch to control the speed of thepump P20. The pump controller P28 is responsive to a high level sensorP34 and a low level sensor P36 on the collecting sump. If the level ofthe slurry in the sump falls below the level of the sensor P36, the pumpcontroller P28 causes the pump P20 to slow down so as to permit thelevel of slurry in the collecting sump P12 to rise. The pump P20 speedsup in response to a rise in the slurry level above the sensor P34.

The sensors P34 and P36 may be of known design and may be combined intoa single unit. Among known sensors are bubbler type sensors andresistance probes. In lieu of sensors producing a high level and lowlevel signal, a sensor providing an error signal when the sump leveldeviates from a preset desired level may be used. The error signal maybe positive, for example, when the level is above the preset desiredlevel and may be negative when the level is below the preset level. Theerror signal would increase in magnitude with increasing deviation ofthe sump level from the preset desired level. The Pump controller wouldrespond to the error signal so as to speed up or slow down the pump tocorrect the sump level.

The discussion will proceed on the assumption that discrete sensors P34and P36 are used to produce a high level and low level signal, it beingunderstood that other sensors could be used instead. The discussion willalso proceed on the simplification that the controllers respond only tothe presence and/ or magnitude of an input signal. In fact, controllerslikely to be used would be more sophisticated and would respondadditionally to delays and to rate of change of system parameters.However, the principles of the invention can be usefully and more easilydiscussed with the aid of the foregoing assumptions.

Returning now to the discussion of the pump controller,

it will be noted that when the pump P20 slows down, the

pressure at the cyclone classifiers P24 tends to drop. This may have theeffect of closing a valve so as to permit the pressure in the cycloneclassifiers to remain within the predetermined limits. Similarly, whenthe level of slurry in the sump rises above the level of the sensor P34,and the sump controller P28 sends a signal to the pump P20 causing it toincrease its output, the pressure controller P26 may open a valve on oneof the controlled classifiers.

The density controller P22 and the pump controller P28 may have astepped operation analogous to that of the sequential opening andclosing of valves caused by the pressure controller P26. In other words,the pressure controller P26 causes stepped increases or decreases inpressure as a result of the sequential closing or opening of valves.Likewise, the density controller P22 may regulate the valve P30 instepped intervals in response to density information. If the densityfalls below a lower limit, the valve P30 may, for example, be turned ina closing direction through one revolution. Likewise, if the densitycontroller senses that the density has risen above a certainpredetermined density, the valve P30 may be opened through one completerevolution. There may be, say, eight or ten revolutions required tocompletely open the valve from a completely shutoff condition.

Similarly, the pump controller P28 may, in response to a high levelsignal from the sensor P34, speed up the pump fiow rate by, say, 10%.Likewise, in response to a low level signal from the sensor P36, thepump controller P28 may slow down the fiow rate of the pump P20 by, say,10%.

It is clear that there is inter-action between the density controllerP22, the pressure controller P26, and the pump controller P28.Basically, the system will be regulated so that first, pressure andsecond, density tend to remain within preselected optimum ranges. Whilethe pressure and density remain within these optimum preselected ranges,the pump controller P28 tends to maintain the level in the collectingsump P12 within a desired range.

However, let us assume that, with pressure and density in the desiredoperating ranges, the collecting sump level rises so that the pumpcontroller P28 has signalled the pump P20 to pump at its maximum outputrate. Let it be further assumed that the level in the sump P12,notwithstanding the maximum output of pump P20, continues to rise andthat a high level signal is transmitted from the high level sensor P34.

In this situation, the only satisfactory way of reducing the level ofslurry in the collecting sump P12 is to reduce the fiow of water via thewater input pipe P32. The water ow can only be reduced if the densitycontroller senses that the density is too low. The density of the slurrycan be made lower by having the cyclone classifiers P24 operate at lowerpressure. At lower pressure, more and coarser particles will fiow out ofthe overflow, with the result that the underflow slurry density willdecrease. Accordingly, the high level signals from the sensor P34 may bepassed onto the pressure controller P26 to adjust the pressure limits tolower levels than would be desired for optimum operation. At these lowerlimits, a high pressure signal will be more readily produced, resultingin the opening of a valve to a further cyclone classifier, which has theeffect of reducing the pressure at which the cyclone classifiersoperate, so as to increase the overfiow slurry density and decrease theunderflow slurry density fed to the primary grinder P14. The result isthat the density of the slurry in the collecting sump P12 will tend todecrease, and the density controller P22 will cause less water to be fedinto the collecting sump, which has the effect of tending to lower thesump level, which is the result desired.

In the foregoing example, the level of the collecting sump was regulatedby overriding the optimum pressure limits and substituting lowerpressure limits for the operation of the cyclone classifiers. It can bereadily seen that other override connections between control units arepossible in practice. The example just given would not be representativeof optimum system design because operating inefficiencies are introducedwhen optimum pressure limits are overridden. It is preferred that thepressure limits be kept at optimum setting and that the pressurecontroller override the density controller when all controlledclassifier valves are open or all such valves are closed and thepressure remains too high or too low, as the case may be. Further it ispreferred that when the density controller has reached one of itsoperational limits (by completely opening or completely shutting off thewater input to the collecting sump) an override control signal should besent to the pump controller to speed up or slow down the pump. Thus, thepump capacity and pump speed range should b e designed to be sufficientto keep the sump level within its limits even when the pressure anddensity controllers are operating at their operational limits.

This preferred system of override controls has the advantage that onlyone override control is provided to any control unit, so that there isno possibility of any unit receiving conflicting override signals fromdifferent units. Further, optimum pressure limits and optimum densitylimits tend to prevail, promoting economy. Finally, the preferred systemenables a convenient override connection from the pump speed controllerof the second grinding stage to the pressure controller of the primarystage, as illustrated in FIG. 3 (which also shows the preferred overridecontrol arrangement within each of the first and second stages).

Referring again to FIG. 2, the secondary grinding stage includes asecondary grinder S14 whose output is fed into a collecting sump S12.Also fed into the collecting sump S12 is the output of the finesoverflow from the cyclone classifiers P24, and a water input S32adjusted by a valve S30 regulated by a density controller S22.

The slurry in the collecting sump S12 is pumped by a pump S through adensity controller S22 to a plurality of cyclone classifiers S24. Thesecyclone classifiers S24 include uncontrolled classifiers and controlledclassifiers and operate in exactly the same manner as the cycloneclassifiers P24 in the primary grinding stage. A pressure controller S26regulates the pressure in the cyclone header of the cyclone classifiersS24 between preselected upper and lower limits, which may be the same asthose established for the cyclone classifiers P24 or which may differ,depending upon the size of the cyclone classifiers used and theoperational requirements of the system.

The overflow output of the cyclone classifiers S24 is fed as a finesoutput to final separators (not shown) which separate the final productfrom the waste. The coarse l output of the cyclone classifiers S24 isfed back to the secondary grinder S14.

In optimum operation of the system, the secondary grinding stage will beoperated at full capacity and the pressure and density of the secondarygrinding stage will be maintained within preselected limits. Internaloverride controls for the secondary stage are preferably analogous tothose of the primary stage, as shown in FIG. 3. The primary grindingstage should for economy be designed to act as a surge with respect tothe secondary grinding state and accordingly should have a capacitysomewhat in excess of the capacity of the secondary grinding stage ofthe operation.

Referring specifically to the internal regulation of the secondarygrinding stage which is similar to the internal regulation of theprimary grinding state, the density controller S22 and pressurecontroller S26 maintain the density and pressure of the secondary systemwithin certain predetermined limits subject to an override connectionfrom the pressure controller S26 to the density controller S22. The pumpcontroller S28 maintains the level of the collecting sump withinpredetermined limits subject to an override connection from the densitycontroller S22. (In lieu of a collecting sump S12, there may be a surgetank in which case the weight of material in the surge tank would bemaintained within certain predetermined limits.)

In addition to the internal control of the secondary grinding stagethere is an override connection from the secondary grinding stage to theprimary grinding stage control units so that the conditions prevailingin the primary grinding stage can be adjusted to make possible thesteady state operation of the secondary grinding stage in its optimumpressure, density and level conditions. This can conveniently beaccomplished by adjusting the pressure standard for controller P26 viaadjustment means P25, corresponding to means in FIG. l. There are twosituations in which feed back from the secondary grinding stage to theprimary grinding stage control units will occur.

These are as follows: i

(l) With the secondary pump S20 operating at maximum output, the sumplevel in the sump S12 nevertheless remains too high and the high levelsensor S34 transmits a high level signal to the pump controller S28. Tocorrect this condition, the high level signal from the sensor S34 issent to the pressure controller P26 to increase limits in the primarypressure controller P26. This tends to cause the closing of a valve inone of the controlled cyclone classifiers P24. The result is that thepressure in the cyclone classifiers P24 will increase so as to forcefiner particles to the outside of the primary cyclone classifiers P24with the result that the overflow has fewer finer particles and theoverflow slurry density decreases. The slurry fed into the collectingsump S12 therefore has a lower density and this lower density will besensed eventually by the density controller S22 which thereupondecreases the amount of water fed by Water input S32 into the collectingsump. Because less water now enters the collecting sump S12, the sumplevel tends to decrease, thereby correcting the adverse condition thatprevailed prior to the transmission of the signal.

(2) Similarly, if the pump S20 were operating at its lowest permittedspeed, and a low level signal were transmitted by the sensor S36, thislow level signal would be passed onto the pressure controller P26 so asto decrease the pressure limits at the primary pressure controller,which would tend to lead to the opening of a valve leading to one of thecontrolled cyclone classifiers P24 so as to permit reduction of pressurein the primary cyclone classifiers. The result would be that coarserparticles would flow out of the overflow and the overflow slurry densitywould increase. This would be sensed eventually by the densitycontroller S22 which would therefore add water via water input S32 andthe level of the sump S12 would increase.

Situation (2) is somewhat unrealistic, and should not occur in aproperly designed system. Optimally, the secondary grinding stagecapacity will be so related to the primary grinding stage capacity, andthe flow-through will be so regulated, that the secondary grinding stagetends to operate at full capacity at a relatively fast pump speed andWith most or all controlled valves of the cyclone classifiers S24 open.

In FIG. 2, the signals sent by high level sensor S34 and low levelsensor S36 to the pressure controller P26 of the primary grinding stagemust pass through AND gates S38 and S40 respectively. Also fed to theAND gates S38 and S40 is a pump limit signal from the pump controllerS28, which signal is present only when the pump controller S28 indicatesthat the' pump speed cannot be further adjusted, i.e., that the pump hasreached its operational limits. Thus, the high level signal from thesensor S34 is transmitted to the pressure controller P26 only in thepresence of a pump limit signal from pump controller S28 indicating thatthe pump S20 is functioning at maximum speed. Similarly, the low levelsignal from the sensor S36 appears in the pressure controller P26 onlyif at the AND gate S40 there is also a pump limit signal from the pumpcontroller S28 indicating that the pump is operating at its slowestspeed. Only a single line is shown transferring the pump limit signalfrom the pump controller S28 and to the AND gates S38 and S40; inpractice it may be necessary to have two discrete lines, or it may bepossible to have a positive limit signal when the pump is operating atits maximum rate of speed and a negative limit signal when the pump isoperating at its minimum rate of speed.

Alternatively, the low level and high level signals can be fed directlyto the pressure controller as well as to the pump controller, and thepump controller can send an inhibit signal to the pressure controllerwhich cancels out the high level and low level signals. The inhibitsignal itself would be cancelled when the pump reaches its operationallimits, in which case the high level signal and low level signal wouldbe operative at the pressure controller to increase or decrease thepressure limits by a preset amount.

The pressure limits prevailing at the pressure controller P26 can thusbe varied upwardly or downwardly through stepped increments as a resultof persistence of a high level or low level signal at the secondarycollecting sump and in the circumstance that the pump S20 has reached anoperational limit. Preferably, a delay device is provided to preventsuccessive adjustments of the pressure limits except after a time delaychosen to permit the system to achieve a steady state condition. Thedelay device can operate in exactly the same manner as the delay devicedescribed with reference to FIG. 1.

If the pressure limits prevailing in the pressure controller P26 havebeen adjusted to a predetermined maximum or minimum, the densitycontroller P22 may be required to alter the density standard in order toprevent completely unsatisfactory pressure conditions in the primarycyclone classifiers. To this end, once the pressure controller P26 hasreached its operational limits, the density controller P22 can becontrolled to vary the permitted density limits so as to regulate thewater input through input pipe P32 and thus to correct the undesiredpressure condition. For example, if the cyclone pressure is too low, thedensity controller may be adjusted to lower the density limits. Theresult will be that the density of the slurry will appear to be too highto the controller and extra water will be admitted via the pipe P32.This tends to raise the sump level, and thus the pump P will speed up,raising the pressure at the cyclone classifiers P24.

In some ore-processing systems, it may be advantageous to maintain bothpressure and density limits in the secondary stage constant, withouthaving an override connection from the secondary pressure controller tothe secondary density controller. In such systems, this may beaccomplished by having the secondary pressure controller S26 send anoverride signal directly to the primary pressure controller P26, as wellas having an override connection from the secondary pump controller S28to the primary pressure controller P26. There would thus be a third andfourth situation in which an override signal would be sent from thesecondary stage to the primary stage, viz,

(3) With all the valves of the controlled cyclone classifiers S24opened, a high pressure signal persists in the pressure controller S26.In this case, the secondary grinding stage is operating at full capacityand therefore it is desired that the primary stage do more grinding. Itis therefore desired to decrease the density of the primary overfiow andaccordingly the primary pressure limits should be increased. Increasingthese limits has the effect of decreasing the primary overflow densityas desired, which will have the effect of lowering the density of theslurry fed into the collecting sump S12. The density controller S22 willtherefore require less water to be fed in by supply pipe S32 into thecollecting sump S12, as a result of which the level in the collectingsump S12 will drop. The drop in level tends to slow down the pump S20,which reduces the flow to the cyclone classifiers S24. The slow down inflow results in a decrease in pressure, as a result of which the highpressure signal will disappear in the pressure controller S26, which iswhat was desired initially.

(4) In the case that all valves of the controlled cyclone classifiersS24 are closed, and a low pressure signal persists in the pressurecontroller S26, the pressure controller P26 will be required to operateat decreased pressure limits. The operation will be the reverse of thatdescribed immediately above in situation No. (3), and the result will bethe eventual elimination of the low pressure signal in the pressurecontroller S26.

Again situation (4) should not occur in a properly designed system-thesecondary stage should be designed to operate at relatively fast pumpspeed with most of the controlled valves of the classifiers S24 open.

It should be noted that the signal permitting the secondary stage highlevel signal or low level signal to pass to the primary grinding stagepressure controller P26 may be derived from the pump controller S28 orcan be derived from the pump S20 directly. This principle appliesequally to the other instances referred to above in which one unitpasses on a signal to another unitfor example, the all valves open orall valves closed signal can be derived from the pressure controller S26or may be derived from limit switches attached directly to the valves.

Instead of having a fully automated feed-back operation as describedabove, it may be preferable in some circumstances to have onlyenunciators advising personnel supervising the process that certainphysical limitations have reached, in which case the personnel couldmake appropriate adjustments of limits. For example, instead of havingpump controller S28 pass on the high level or low level signal directlyto the pressure controller P26 when the pump S20 has reached anoperational limit, an operator could be signaled that the pump S20 wasoperating at an operational limit. The operator could then make thedecision to adjust the limits in the pressure controller P26 or to takesuch other action as might rectify the undesirable situation.

The foregoing discussion has proceeded on the basis that an undesirablesituation in the secondary grinding stage has been corrected firstly byadjustment of the pressure limits in the primary grinding stage pressurecontroller P26. It will be noted that instead of transmitting theoverride signal or signals from the secondary grinding stage to theprimary pressure controller P26, these signals might have been fed backinstead to the density controller P22 or to the pump controller P28.However, in most instances it will be found best to adjust primarypressure limits rather than primary density or pump speed.

One reason for this is that the cyclone classifiers P24 can be made towork reasonably satisfactorily over a fairly wide range of pressures,notwithstanding the fact that there is an optimum range to which thepressure limits initially correspond. Secondly, such arrangement permitsthe preferred override system within the primary grinding stage.Further, feed-back of the secondary grinding stage information to thepump controller P28 tends not to have a completely desirable result,because the initial effect on the secondary grinding stage does notcoincide with the effect on the secondary grinding stage following thereadjustment of the primary grinding stage to the difference in thespeed of the pump P20. This can be best illustrated by an example.Suppose that with the pump S20 operating at maximum output, the sumplevel in the collecting sump S12 is still too high. Then the high levelsignal produced by the sensor S34 would be passed on to the pumpcontroller P28. The pump controller P28 could be ordered to speed up orto slow down the pump P20. Let us suppose that it is ordered to speedup. This will have the immediate effect of passing a greater flow offluid through the cyclone classifiers P24 which will result in a greatervolume of slurry being introduced into the collecting sump S12. This hasthe immediate effect then of worsening the situation at the collectingsump S12. On the other hand, if the pump P20 is ordered to slow down,the immediate effect on the collecting sump S12 will be beneficial butthe steady state effect may not be satisfactory. When the pump P20 slowsdown, the pressure drops at the cyclone classifiers P24. This has theeffect of increasing the overflow slurry density. The increased densityof the overliow could, when sensed by the density controller S22 lead tothe introduction of more water via input S32 into the collecting sumpS12. The greater volume of water input may be sufficient to offset thereduced input flow of slurry and the result may be that the situation inthe collecting sump S12 has not been improved.

It is diflicult to predict, without reference to an actual physicalplant, the optimum stepping operation of the limits in the pressurecontroller, density controller, or pump controller. The amount by whichthe limits set in any one of these control units varies in response to afeedback signal will depend upon many factors, including the relativecapacities of the two systems; the flow rate, the length of timerequired for a change in operation of the primary stage to affect theconditions prevailing in the secondary stage, etc. However, as a generalrule, the steps should not be too great with respect to the optimumdesired conditions. For example, adjustments in pressure limits shouldbe of an order of magnitude comparable to and preferably less than thechange in operation which results from the opening or closing of asingle valve of a controlled cyclone classifier.

Complete control of the system is effected by the provision of anoverflow pipe S42 leading from the collecting sump S12 to the collectingsump P12. Thus, if conditions at the secondary grinding stage are suchthat the secondary grinding stage cannot handle the slurry fed to it,the overflow slurry will be simply fed back to the collecting sump P12and will not escape as waste. The slurry can then be reprocessed throughthe primary grinding stage.

FIG. 4 illustrates the manner in which the control devices of FIG. 2interact with conventional ore-processing apparatus in a completeore-processing system.

Referring to FIG. 4, an ore processing system utilizing the inventiveapparatus is shown in block diagram form. The particular process to bedescribed is an iron-ore process using magnetic concentrators andseparators, but it is to be understood that this is by way of exampleand that details of the method and apparatus may be modified to meet therequirements of different processes.

This system embodies a two-stage grinding process, the first stageutilizing a wet mill 42 and the second a ball mill '82.

The mill 42 is fed by a plurality of cyclone classifiers 60 and the mill82 by cyclone classifiers 80.

The mill 42 grinds crude ore in slurry fed from an ore input 40 andregrinds the relatively coarse particles in slurry fed from theunderflow of the cyclone classifiers 60. The slurry, after passingthrough the wet mill 42, is then passed through a screen classifier 44.The coarser material is returned via conduit 48 to the ore input 40 forreprocessing and the fines are fed into a sump 46 and then pumped by apump 47 to magnetic separators 49. The tailings from the magneticseparators 49 are dumped into a tailing sump 50.

The slurry containing the ore is fed from the separators 49 to amagnetic concentrate sump 52 and then pumped by a pump 53 via a densitycontroller 55 to a cyclone header 56 which distributes the slurry to theplurality of cyclone classifiers 60. Some of these classifiers, as isshown in FIG. 5, are uncontrolled and therefore in use at all timeswhile others, the controlled classifiers, are in use only when theirassociated control valves V1, V2, V3, V4 are open. FIG. 4 shows only asingle block representing the cyclone classifiers 60 but it isunderstood that it refers both to controlled and uncontrolled cycloneclassifiers.

The overflow (the fines) from the cyclone classifiers 60 are fed into acollecting sump 74. The slurry from collecting sump 74 is pumped by apump 75 through a density controller 78 to the plurality of cycloneclassifiers 80. These classifiers 80 send their underfiow (containingthe coarse material) through the ball mill 82 for fine grinding. Theoutput of the ball mill 82 is fed back into the collecting sump 74.

The overflow fines from the cyclone classifiers 80 are passed through ahydro separator 90 and thence via a pump 92 to a final magneticseparator 94 whose output containing the ore concentrate is deposited inthe final concentrate sump 96. Tailings from both the hydro separator 90and the magnetic separator 94 are dumped into the tailing sump 50.

The description of FIG. 4 to this point is a description of aconventional ore processing system of a type known in the art, exceptthe use of controlled and uncontrolled cyclone classifiers.

As mentioned previously, it is desirable for efficient operation of thecyclone classifiers to keep the pressure at the input of the cycloneclassifiers within a set range.

To this end, the differential pressure across the cyclone classifiers 60is measured in the pressure transducer 54 conveniently attached to thetop of the cyclone header 56. The differential pressure between theheader 56 and the atmosphere is converted to an electrical signal whichis transmitted from the pressure transducer 54 to a comparator 64. Thepressure drops due to the cyclone header outlet and cyclone input valvesmust be taken into consideration, in order to obtain the actual cyclonedifferential pressure.

The comparator 64 receives the signal from the pressure transducer 54 asan input, compares said signal with a variable pressure standard. Ifsaid pressure signal indicates a pressure falling outside predeterminedlow and high dead band limits on either side of the variable pressurestandard, the comparator 64 sends a low or high pressure signal,depending on whether the pressure is below or above the limits, to atimer 62.

An increase in the variable pressure standard increases thepredetermined pressure limits at which the high and low pressure signalsare produced by comparator 64. Conversely, when the variable pressurestandard decreases, the predetermined pressures at which the high andlow pressure signals are produced by the comparator 64 are decreased.The dead band limits remain at a uniform pressure differential on eachside of the pressure standard notwithstanding changes in the pressurestadard, and thus the pressure differential between the predeterminedpressures producing the high and low pressures signals is constant. Thedead band limits are designed to accommodate the pressure range overwhich the cyclone classifiers operate efficiently during normal oroptimum operation.

A pressure transducer, comparator, and timer must be provided also forthe cyclone classifiers 80. These devices are shown simply as a singlepressure controller 83 for simplification of description. However, whilethe pressure controller for the primary grinding stage will be designedto permit adjustment of the pressure standard, the pressure controller83 is preferably designed to permit only manual adjustment of thepressure standard. The reason for the difference between the twopressure controllers as explained above with reference to FIG. 2, isthat for efficient operation of the system, the secondary grinding unitmust always be operating at full capacity and at optimum operationalconditions. To this end, the pressure and density in the secondarycyclone classifiers are kept within predetermined optimum limits, andany variation from secondary optimum operation is corrected in thprimary stage rather than in the secondary stage.

Two proposed embodiments of the timer 62 are described in detail laterwith reference to FIGS. 7 and 8. Essentially the timer includes a devicewhich controls the sequential opening and closing of the cyclone controlvalves (e.g., V1, V2, V3 and V4, shown in FIG. l) and a delay devicewhich will not permit a second opening or closing of a control valvewithin a specified period of time following a first opening or closingof a valve. This delay interval prevents immediate reaction to thetransient pressure changes in the system following the opening orclosing of a cyclone classifier control valve so that the system hastime to stabilize itself.

The timer 62 responds to the low pressure signal from the comparator 64to cause the closing of a predetermined open control valve (i.e., one ofthe valves shown in FIGS. 1 and 3 as V1, V2, V3, and V4). Similarly ahigh pressure signal from the comparator 64 will be converted by thetimer 62 into a valve-opening operation a predetermined closed controlvalve. Thus the input pressure at the cyclone header is kept withincertain predetermined limits rendering the operation of the system moreefiicient.

As stated previously with reference to FIG. 2, it is necessary to keepthe levels of the slurry in the magnetic concentrate sump 52 and in thecollecting sump 74 within a specified range. To accomplish this, each ofthe sumps is provided with high level and low level sensors whichproduce a high level signal when the sump level is too high and producea low level signal when the sump level falls below the predetermined lowlevel. In the first instance, the sump level information is transmittedto pump controller 51 and pump controller 73 respectively which vary thespeed of the pumps 53 and 75 so as to tend t0 maintain the slurry levelin the sump within the predetermined limit.

Also as stated above, in certain instances the sump level informationfrom the sump 74 may be fed back as an information input to thecontrollers of the primary stage. This is accomplished as follows:

The collecting sump 74 is tted vwith a high level sensor 86 whichproduces a high level signal, and a low level sensor 84 which produces alow level signal. The signals from the level sensors 84, 86 aretransmitted first to the pump controller 73 and, when the speed of thepump 7S reaches an operation limit, the high level or low level signalsmay be passed onto the comparator 64. The signals from the level sensors84, 86 vary the variable standard pressure in comparator 64, in a mannerwhich can be understood more readily when explained with reference toFIG. 6, which graphically illustrates the operation of comparator 64..The base line XY represents a pressure scale lwith pressure increasingfrom left to right. Points A and B on the pressure scale XY representthe lower and upper dead band limits respectively of the preferredvariable pressure standard C. The initial pressure at the input of thecyclone classifiers 60 will `be assumed to be at the point P.

Assume that the cyclone input pressure drops from the point P to A. Thepressure is now at the lower dead band limit A of the variable set pointC so that the comparator 64 sends a low pressure signal to the timer 62.The timer 62 closes a valve and thus increases the cyclone inputpressure.

Similarly if the pressure increases above the upper limit B thecomparator 64 will send a high pressure signal to the timer `62 whichwill then open a control valve and reduce the pressure in the cycloneheader 56.

Now assume, with the initial pressure at P, that a high level signal issent from the high level sensor 86 to the comparator 64, with the pump75 operating at maximum speed. The high level signal moves the variablepressure standard from C to C so that the new lower dead band limit Alies above the original pressure P.

The pressure P now falls outside the range AB so that the comparator 64sends a low pressure signal to the timer 62. The timer 62 closes a valveto increase the pressure at the inputs to the classifiers. The resultingsteady-state pressure indicated by the pressure transducer signal to thecomparator 64 is, say, at P on the pressure scale. As stated previouslyan increase in pressure forces more lines to the outside of a cycloneclassifier. Therefore the overflow coming from cyclone classifiers 60 tothe collecting sump 74 contains fewer lines per volume of water and thusthe density of slurry entering the collecting sump 74 is lower. As aresult, the density controller 78, which controls the water valve 79 onthe water input 81 to the sump 74, allows less water to pass into thecollecting sump, in order to increase the density. Thus, the level ofcollecting sump 74 drops and the high level sensor 86 ceases to send ahigh level signal.

Conversely, at pressure P and dead band limits A, B, if when the pump 75is running at its lowest speed a low level signal is sent from low levelsensor 84 to comparator 64, then the variable pressure standard is movedfrom C to C so that new dead band limit B falls below the pressure P.Thus the comparator 64 sends a high pressure signal to the timer 62which then opens one of the cyclone classifier control valves V1, etc.As a result, the pressure indicated by the pressure transducer 54decreases to a point on the pressure scale, say P", the density of thefines in the overow from the cyclone classifier 60 increases and thusthe density of slurry in collecting sump 74 increases. The densitycontroller 78 accordingly adjust the valve 79 to add more water,increasing the level in the sump 74, whereupon the low level sensor 84stops sending a low level signal.

The variation of the pressure standard in the pressure comparator 64,initiated by either the high level signal or the low level signal,should in general be sufficient to operate a valve. The means forvarying the pressure CTI standard may be, for example, a potentiometerwhose movable contact is operated by a servo-motor which is caused tomove in one direction by the high level signal and in the otherdirection by the level signal. The servomotor may be turned off, forexample, by the opening or closing of a valve, by the operation of thedelay device, or in any other convenient manner following the desiredactuation of a valve. The servo-motor then remains off until the nextfollowing high level signal or low level signal, after the expiration ofthe delay period. Instead of a potentiometer of servo-motor, otherdesired known means for varying the pressure standard could be used.

As discussed with reference to FIG. 2, the high level, maximum pumpspeed situation in the secondary stage may occur from time to-time, butwith proper design of the units, the low level, minimum pump speedsituation should rarely, if ever, occur.

The inter-relationship of the other control units, already describedwith reference to FIG. 2, :will not be described with reference to FIG.4, as it is believed that the manner in which these control unitsinteract with the other apparatus in an ore processing system will beclear to the reader who has followed the discussion so far.

The foregoing discussion has proceeded on the premise that both theprimary and secondary grinding stages are wet stages. However, controlof a secondary wet stage in accordance with the invention may beeffected in the manner described above, in the case where the primarystage is a dry stage using, for example, a rotary forcedair type ofgrinding mill, whose lines output is fed into a collecting sump or surgetank and fed to the secondary cyclone classifiers as a slurry.

In the case of a dry primary stage, any override controls from the wetsecondary stage to the dry primary stage must of necessity be adapted tothe different operational parameters and control devices utilized in theprimary stage. For example, the override control from the secondary pumpcontroller might be applied to the main fan damper of the primaryforced-air rotary mill, or to the speed controller for a magneticdrum-type rotary separator, in order to increase or decrease the finesoutput portion of the primary grinding mill to meet secondary stagerequirements.

FIG. 7 is a schematic drawing of one proposed embodiment of the timer 62shown in FIG. 4.

The timer of FIG. 7 employs a reversing motor MT, driving cams CA, CB,CC, C1, C2, C3 and C4, mounted on a single shaft, three auxiliary timersTH, TL and TX, and relay switches associated with said cams and timers.The timer controls solenoids RV-l, RV-Z, RV-3 and RV-4 which open andclose valves V1, V2, V3, and V4 respectively. When the solenoids areenergized, the valves are open; when the solenoids are deenergized, thevalves are closed.

The cams are notched so that when a notch corresponds to the contact ofthe associated switching lmechanism the switch is opened. At all othertimes it is closed.

In FIG. 7, the 0 position for all the cams is, the lower end of thevertical axis, and the angle of rotation increases as the cams move inthe clockwise direction. Carn CA has notches at the 0, 90, 180 and 270positions. Cam CB has a single notch immediately before the 0 position.Cam CC has one notch immediately after the 0 position. Cam C1 has onenotch extending from the 0 to the 90 positions, cam C2 has one notchextending from the 0 position, to the 180 position, cam C3 has one notchextending from the 0 position to the 270 position and cam C4 has asingle bump at about the 355 mark, Le., it is notched from 0 almost to360.

A high pressure signal from the comparator 64 shown in FIG. 4 closesswitch SH and holds it closed until the pressure is reduced to apressure below the upper dead band limit. The closing of switch SHcloses a circuit through timer TH and normally-closed switch SX from apotential terminal P to ground. Timer TH is energized thus closing thetwo switches it controls, viz., switches SH1 and SH2. These switcheswill remain closed as long as TH is energized and for a short interval,say 3 seconds, after timer TH is denergized. With the closing of theswitch SH1 two more circuits are closed between the potential line P andground. One circuit leads through switch SH1 and running coil J of motorMT and the other through switch SII-I1 and timer TX which is in parallelwith running coil J. Timer TX, when energized, opens normally-closedswitch SX. This switch will remain open while timer TX remains energizedand additionally remains open following deenergizing of timer TX for thespecified delay interval required for stabilization of the system afterthc opening or closing of a valve, say minutes. The opening of switch SXcauses the deenergization of timer TH and the subsequent opening ofswitches SH1 and SH2 three seconds later (say).

When switch SHZ is closed, through switch SCB, a circuit is closedbetween the potential line P` and ground through the one-half K of thesplit eld coil in motor MT. When the running coil J is conductingcurrent the energized half coil K will start the motor MT in, say, theclockwise direction. The motor MT will have its running coil J activatedthrough switch SH1 until, say, 3 seconds after timer TH is deenergized.By that time the shaft supporting the cams will have rotated sucientlyso that cam CA will have closed a normally-open switch SCA. Switch SCAwill remain closed and the cams will continue to rotate until cam CAreaches the 90 notch which opens switch SCA and stops the motor MT.

Assume that all valves V1 to V4 shown in FIG. l and F IG. 3 are closed.Then, after rotating through 90, cam C1 will close the switch SC1. Thus,there is a closed circuit between the potential line P and groundthrough switch SG1 and coil RV1. Coil RV1 is energized, opening valveV1.

It can be seen that another high pressure signal after the delayinterval would tuin the shaft through another 90 to the next notch oncam CA, (there being one notch that will open switch SCA every 90) thecam CZ closing switch SC2 (switch SC1 remaining closed), therebyenergizing coil RVZ and thus allowing another valve V2 to open.

It a similar high pressure signal persisted after the prescribed delayinterval then switch SC3 and, ultimately, switch SC4 would be closed bycams C3 and C4 respectively, thus opening the valves V3 and V4 referredto above.

When all the valves have been opened (i.e., the cams have been rotatedthrough almost 360, say 355) cam CB will open the switch SCB, which willinterrupt the circuit to eld coil K thus preventing the motor MT fromturning any farther in the clockwise direction. Means (not shown)responsive to the opening of the switch SCB may signal the operator thathe has no more valves to open.

Conversely, when a low level pressure signal is sent from the comparator64 to the timer 62 (both of which are shown in FIG. 4) switch SL isclosed completing the circuit through switches SL and SX and timer TLfrom the potential line P to ground. Thus the timer TL is energizedclosing switchesl SL1 and SLZ for an interval extending a short timeafter the timer TL is deenergized, say 3 seconds. With switches SL1 andSLZ closed, running coil J of motor MT will be energized through switchSCC and the switch SLZ in the opposite direction to that of current ilowthrough half coil K and therefore the starting impulse is in theopposite direction, i.e., counterclockwise. As before, timer TX isenergized, opening switch S-X which opens a circuit through timer TLcausing it to become deenergized and thus it allows switches SL1 and SLZto open. Running coil I is energized by electric current first throughswitch SL1 and then switch SCA until cam CA has rotated back through 90,opening the switch SCA. When the motor MT stops, one of cams C1 to C4(depending upon the initial conditions of the circuit) will have reachedthe notch which allows the corresponding closed 18 switch SC1 to SC4 toopen thereby deenergizing the associated coil RV1 to RV4 and closing theassociated valve V1 to V4.

When the last valve V1 in the sequence closes, cam CC has rotated farenough to open the switch SCC thus preventing the motor MT from turningany farther in the counterclockwise direction and also may send awarning signal to the operator by means (not shown) responsive to theswitch SCC, that he has no further control valves to close.

Cam CA has an extended notch at the 0 position so that the motor whenturning clockwise will be stopped at the same time that cam CC opensswitch SCC and, when turning counterclockwise, will be stopped at thesame time that cam CB opens switch SCB. This prevents the shaft fromactually reaching the 0 mark, from either direction. If the shaft couldreach the 0 mar-k, no further operation would be possible because of thepositions of the notches on cams CB and CC.

Although only four cyclone feeder control valves are shown in FIGS. 1and 5 and discussed in the description of FIG. 7, it may be seen thatmore control valves may be added by adjusting the cam angles of cams C1,CZ, etc. and by adding notches to the cam CA. Thus for six valves thecam CA would be notched every 60. For the cyclone classifiers 60 innormal operation, valves V1 and V2 may be open and valves V3 and V4 myabe closed. Under all but extreme circumstances it is assumed that forthe system described, the opening or closing of two more valves will besuicient to correct any pressure or level problems. If this is not thecase more controlled conduits should be provided.

FIG. 8 is a schematic drawing of another proposed embodiment of thetimer 62 shown in FIG. 4.

This device comprises two timers and pluralities of latching relays,unlatching relays and relay switches, which control solenoids RV1, RVZ,RV3 and RV4 that open associated valves V1, VZ, V3, V4 when energizedand close the valves when deenergized.

A high pressure signal from the comparator 64 closes a switch RH whichwill stay closed until the high pressure signal stops. If the normallyclosed switches RA1 and RB1 are closed, there will now be two closedcircuits be tween a potential line Q and ground, one through switchesRH, RA1 and RB1 and a timer TA and the other through said switches and alatching coil L1. When latching coil L1 is energized, it closes andlatches switch RL1 responsive to coil L1 thus closing the circuitbetween potential line Q and ground through coil RV1 and activating coilRV1, thereby opening control valve V1 (shown in FIGS. l and 3). Whenvalve V1 opens it causes a limit switch SIA to close and another limitswitch S1B to open.

At the same time as coil L1 is energized timer TA is energized openingthe two normally closed switches RA1 and RAZ which it controls, therebycutting oi current to timer TA and coil L1. These switches RA1 and RAZstay open for a specified delay interval (say 5 minutes), surticient forstabilization of the system after opening a valve, thus prevent theopening or closing of any valves during said delay interval.

IIf a high pressure signal persists after the delay interval haselapsed, switch RA1 becomes closed again and once more circuits will beclosed through timer TA, through latching coil L1 (which has no effectbecause contacts RL1 are still locked shut), and through limit switchSIA and a latching coil LZ. When timer TA is energized it will againopen RA1 and RAZ for said delay interval. When latching coil L2 isenergized it closes and latches the switch RLZ which it controls thusactivating coil RVZ and thereby opening valve V2. Valve VZ on openingcloses a limit switch SZA and opens a limit switch SZB.

Similarly if the high pressure signal persists after the specified delayinterval a latching coil L3 is activated closing and latching a switchRLS which it controls, activating a coil RV3, thus opening valve V3which closes a limit switch S3A and opens a limit switch S3B.

If the high pressure signal still persists a latching coil L 4 isactivated closing and latching a switch RL4 which it controls,activating coil RV4 which opens control valve V4. Valve V4 opens a limitswitch S4B and closes a limit switch S4A which closes an indicatingcircuit (not shown) which warns the operator that he has no more valvesto open.

Now assume, with all the valves open and switches RAZ and RB2 closed,that a low pressure signal is sent from the controller 64. The signalwill cause switch RL to close thus closing a circuit between potentialline Q and ground through a timer TB and an unlatching coil UL4. As soonas timer TB is energized it opens switches RBI and RBZ and holds saidswitches open for a specified delay interval that may be the same as thedelay interval for timer TA. Unlatching coil UL4, which is energized atthe same time as timer TB, unlatches the contacts RL4 therebydenergizing coil RV4 which causes control valve V4 to close. When valveV4 closes, it causes limit switch S4B to close. This allows anunlatching coil UL3 to be energized when the next low pressure signal istransmitted, and causes limit switch S4A to open, thereby discontinuingthe warning signal.

If, after the delay interval, there is a low pressure signal, switch RLwill close, timer TB will be energized and will respond as above, andunlatching coil UL3 will be energized through switch S4B. Unlatchingcoil UL3 will unlatch switch RL3 thereby, deenergizing coil RV3 andcausing control valve V3 to close. The closure of valve V3 closes limitswitch S3B and opens limit switch S3A.

Note that in this state of the system with switch S3A latching contactsRL1 and RL2 closed, the only latching circuit that would respond to ahigh pressure signal would be that associated with latching coil L3.With unlatching coils UL4 and UL3 already activated, switch S3B closedand switch S2B open, the only unlatching circuit that could respond to alow pressure signal would be that associated with unlatching coil ULZ.Therefore, in response to a low pressure signal the last opened valve(which is still open) is the only one that can be closed and in responseto a high pressure signal the last closed valve (which is still closed)is the only valve that can be opened. It can be seen that the above isapplicable mutatis mutandis, no matter how many valves are opened orclosed.

Assuming that a low pressure signal persists, the closing of switch RLactivates unlatching coil UL2 which will unlatch switch RLZ therebydeenergizing coil RVZ and causing valve V2 to close. When valve V2closes it causes the limit switch S2B to close and the limit switch ,52Ato open.

A further low pressure signal causes R1 to close, energizing unlatchingcoil UL1 thereby unlatching switch RL1 which deenergizes coil RVl thusclosing valve V1. Valve V1, when it closes, causes switch S1A to openand switch S1B to close an indicating circuit (not shown) whichindicates to the operator that he has no more valves t close.

Using the timer shown in either FIG. 7 or FIG. 8 it may be seen that inthe event of a power failure all coils RV1 to RV4 would be deenergizedthus closing all the cyclone classifier control valves. This tends toprevent overflow of the sumps.

I claim:

1. Apparatus for controlling the pressure of slurry introduced from acommon input into a plurality of cyclone classifiers, comprising aplurality of control valves each respectively associated with acorresponding one of said cyclone classifiers permitting the slurry toflow through the corresponding cyclone classifier when the respectiveassociated control valve is open and blocking flow of slurry through thecorresponding cyclone classifier when the respective associated controlvalve is closed, a pressure transducer in the vicinity of the commoninput and responsive to said slurry pressure and producing an outputSignal representing said slurry pressure, a pressurecom! paratorresponsive to the output signal of the pressure transducer and producinga high pressure signal when said slurry pressure reaches a predeterminedhigh pressure limit and producing a low pressure signal when said slurrypressure falls to a predetermined low pressure lirriit, valve-closingmeans responsive to said low pressure signal and closing said valvescontinually and sequentially when the low pressure signal is present,valve-opening means responsive to the high pressure signal and openingsaid valves continually and sequentially when the high pressure signalis present, and delay means responsive to actuation of both saidvalve-operating means and preventing said valve-operating means fromoperating for a predetermined time interval following the last openingor closing of a valve notwithstanding the production of a low pressuresignal or a high pressure signal during said interval.

2. Apparatus as defined in claim 1, wherein the valveopening means andthe valve-closing means for each Valve are combined in a singlevalve-operating means capable of opening and closing the valve.

3. Apparatus as defined in claim 1 wherein the comparator is responsiveto a variable pressure standard input thereby to increase thepredetermined high pressure and low pressure limits at which the highpressure signal and low pressure signal are produced when the pressurestandard increases, and to reduce the predetermined pressures at whichthe high pressure and low pressure signal are produced when the pressurestandard decreases.

4. Apparatus as defined in claim 3, wherein the pressure differentialbetween the predetermined high pressure and low pressure limitsproducing said high pressure signal and said low pressure signal isconstant notwithstanding variation of the pressure standard.

5. Apparatus as defined in claim 4, wherein the pressure sensed by thepressure transducer is the pressure of the slurry in a distributorcomprising said common input to said cyclone classifiers.

6. ln the ore-processing art, apparatus for controlling the pressure ofslurry fed into a distributor for a plurality of cyclone classifiers,comprising a plurality of classifiers fed by this distributor anduncontrolled as to fiow of slurry therethrough, a plurality ofclassifiers each having an associated valve controlled so as to beopenedor closed to fiow of slurry therethrough and fed by thedistributor, and a pressure controller responsive to the pressure of theslurry in the distributor and sequentially opening said controlledclassifiers when the slurry pressure exceeds a predetermined highpressure limit and sequentially closing said controlled classifiers whenthe slurry lpressure lies below a predetermined low pressure limit, thepressure controller including delay means interrupting the sequentialoperation of the controlled classifiers for a pre-set delay periodfollowing the opening or closing of any of the controlled classifiers,the pressure controller including (1) a pressure transducer sensing thepressure'of the 'slurry in the distributor and producing an electricalsignal representative of the slurry pressure, (2) a pressure comparatorreceiving as inputs the transducer output signal and a signalrepresentative of a pressure standard and sensing the difference betweenthe two inputs,l and (3) valveoperating means responsive tothedifference sensed by the comparator and opening the valves sequentiallywhen the comparator senses that the slurry pressure exceeds the pressurestandard by more than a first predetermined amount therebyveXceeding thehigh pressure limit and closing the valves sequentially when thecomparator senses that the slurry pressure lies below the pressurestandard by more than a second predetermined amount thereby lying belowthe low pressure limit.

7. Apparatus as defined in claim 6, wherein the sum of the first andsecond predetermined amounts is of the order of the pressure standarddivided by the average number of classifiers passing slurrytherethrough.

21 22 8. Apparatus as dened in claim 7, wherein the rst FOREIGN PATENTSand second predetermined amounts are the same. 667,142 2/1952 GreatBritain 9. Apparatus as defined in claim 6, additionally including meansfor adjusting the pressure standard in response FRANK W LUTTER PrimaryExaminer to one or more parameters of an ore-processing system. 5 ROBERTH ALPER, Assistant Examiner U.S. Cl. XR.

References Cited UNITED STATES PATENTS 1,890,070 12/1932 Whiton 55-344 X2,119,478 5/1938 Whiron 55-344 X 10

